Evaluation of ultimate strength of post-tensioned anchorage zones

The anchorage zones of post-tensioned concrete members can be divided into local and general zones. The present study estimated the ultimate strengths of post-tensioned beams tested to anchorage failure using the AASHTO LRFD approximate stress analysis/design method, the critical section concept in which the strengths of the node-strut interface and local zone-general zone interface are examined, the bearing strength equation which considers the confinement effect due to reinforcing bars, and the nonlinear strut-tie model approach which incorporates nonlinear techniques in the selection, analysis, and verification processes of a strut-tie model, thereby evaluating their respective validity in the analysis and design of post-tensioned anchorage zones. The ultimate strengths of the post-tensioned beams in the nonlinear strut-tie model approach were estimated by checking the occurrence of a nodal zone failure mechanism, the structural instability of the selected strut-tie model due to the strength reduction of the struts and ties during the incremental loading steps, and conformity to the strut-tie model's geometric compatibility condition.